Aliphatic polyesters represented by polylactic acid, polyglycolic acid, etc. are excellent in biodegradability. Especially polyglycolic acid (hereinafter sometimes referred to as “PGA”) is excellent in heat resistance, gas-barrier property, mechanical strength, etc., so that application thereof for providing various sheets, films, containers, injection molding articles, textiles, fine particulate materials, etc., by itself or as a composite material with another resin material.
For the purpose of improving heat stability in melt-processing, such an aliphatic polyester resin is compounded with a phosphoric acid ester, followed by melt-kneading, to produce an aliphatic polyester composition (for example, Patent documents 1-2).